AP news agency reports he is Robert Bowers, citing law enforcement official

Trump says attack would not have happened if synagogue had armed guards

20:35

Theresa May says she is "deeply shocked"

20:31

The president says he will still go to a political rally later because he cannot let evil people "change our schedule".

20:16

Donald Trump has condemned the 'wicked act of mass murder'

"As you know, earlier today there was a horrific shooting targeting and killing Jewish Americans," the president said.

"This wicked act of mass murder is pure evil, hard to believe and frankly something that is unimaginable.

"Our nation and the world are shocked and stunned by the grief.

"This was an antisemitic act.

"You wouldn't think this is possible in this day and age.

"Our minds cannot comprehended the cruel hate and the twisted malice that could cause a person to unleash such terrible malice during a baby naming ceremony."

He calls antisemitism "vile and hate-filled" and says there must be no tolerance for any form of religious hatred.

"We are praying for the families of the victims," says Mr Trump.

He says the officers injured have been "very badly wounded".

"We mourn for the unthinkable loss of life today."

20:08

19:59

Actor Ben Stiller has responded to Donald Trump's suggestion that armed guards in the synagogue may have been able to stop the gunman from killing people

19:58

Public safety director Wendell Hissrich says the crime scene is one of the worst he has ever seen

19:54

Benjamin Netanyahu 'heartbroken'

19:50

President may cancel campaign rally

Donald Trump says he may cancel a political rally in Illinois on Saturday after the deadly shooting in Pittsburgh.

"You can say we're considering it," he told journalists.

Mr Trump has arrived in Indianapolis to speak at the Future Farmers of America convention.

19:42

Trump: A lot of people have died

President Donald Trump says "a lot of people" were killed in the shooting at a Pittsburgh synagogue.

He said it "looks definitely like it's an antisemitic crime."

The president told reporters at the airport in Indianapolis that what "happened today is a horrible, horrible thing."

He says the FBI is now involved and there were "a lot of people killed" and "a lot of people very badly wounded."

He also says the crime scene is one of the worst many professionals have seen.

Police have a suspect in custody after Saturday's attack at the Tree of Life Congregation.

A gunman opened fire during a baby naming ceremony, killing an unknown number of people and wounding six others, including four police officers.

19:40

Donald Trump says an armed guard in the synagogue may have been able to stop the gunman

19:30

Police rapid response team members responding to the site of the mass shooting

19:25

Synagogue is hub of Pittsburgh's Jewish community

The synagogue is located at the intersection of Wilkins and Shady avenues.

The tree-lined residential neighbourhood, about 10 minutes from downtown Pittsburgh, is the hub of Pittsburgh's Jewish community.

19:15

'Israel is deeply pained'

Israeli Diaspora Affairs Minister Naftali Bennett said he would travel to Pittsburgh to offer his support to the Jewish community there and that he has instructed his team to prepare any assistance that might be required.

In a statement, he said: "The State of Israel is deeply pained by this terrible antisemitic murder.

"Our Jewish brothers and sisters came under a murderous attack while at prayer.

"Our hearts go out to the families of those killed, and we pray for the swift recovery of the injured, as we pray this is the last such event."

19:08

'My heart breaks' - Melania Trump

The US First Lady has responded to the shooting.

She said: "My heart breaks over the news out of #Pittsburgh. The violence needs to stop. May God bless, guide & unite the United States of America."

18:48

'We must unite against hatred and evil'

Ivanka Trump - a convert to Judaism - has issued a statement in response to the shooting.

She said: "All good Americans stand with the Jewish people to oppose acts of terror and share the horror, disgust & outrage over the massacre in Pittsburgh.

AP news agency reports he is Robert Bowers, citing law enforcement official

Trump says attack would not have happened if synagogue had armed guards

18:32

Suspect named as Robert Bowers: A law enforcement official has told AP news agency that the suspect has been identified as Robert Bowers.

US media reports that he is 46-years-old.

18:31

WATCH: Trump uses shooting to defend gun laws

18:30

World leaders respond to attack

French President Emmanuel Macron and Canadian counterpart Justin Trudeau have sent their condolences to victims of the attack.

Mr Truedeau tweeted: "Canadians’ hearts are with the Jewish community in Pittsburgh today, as they endured a horrific anti-Semitic attack while at prayer.

"May the families of those murdered be comforted, and may the injured recover quickly and fully."

Speaking after a summit on Syria with Turkish President Tayyip Erdogan, German Chancellor Angela Merkel and Russian President Vladimir Putin, Mr Macron said: "I would like to express our sadness and support to American people."

18:27

Four police officers injured

Of the six people confirmed to have been injured, four are police, public safety director Wendell Hissrich confirmed.

The gunman has been taken to hospital, but there is no update on his identity - despite reports emerging in US media.

Mr Hissrich added that "there appears to be no active threat to the community".

"I am heartbroken and shocked by the murderous attack today at a synagogue in Pittsburgh," he tweeted.

"The whole of Israel grieves with the families of the dead. We stand together with the Jewish community of Pittsburgh, we stand together with the American people in the face of this horrifying anti-Semitic brutality.

"We all pray for their rapid recovery."

18:19

'The scene is very bad inside'

Wendell Hissrich, Pittsburgh public safety director, has described the scene inside the synagogue as "very bad".

He describes it as "one of the worst I've seen", including plane crashes.

He has confirmed multiple fatalities and at least six people injured, four of whom are police officers.

18:17

There will be a 'lengthy' crime scene in place at the synagogue, police say

18:16

Police will hold a press conference at 4pm local time (9pm BST)

18:05

Synagogue was hosting a baby naming ceremony

The Pennsylvania attorney general has said the shooter "claimed innocent lives".

It happened at a baby naming ceremony and the shooter shouted "all Jews must die", Reuters reports, citing local media.

18:03

Key points:

At least eight dead at Jewish baby naming ceremony in Pittsburgh

Incident at Tree of Life Synagogue left six injured, four are police

Shooter is in custody, reportedly shouted 'all Jews must die' during attack

Trump says attack would not have happened if synagogue had armed guards

Police deployed to other synagogues as a precaution

18:01

More from President Donald Trump

Another line from the president, who spoke to reporters before leaving for a series of campaign events in Indiana and Illinois.

"It's a terrible, terrible thing what's going on with hate in our country frankly, and all over the world," he said.

"Something has to be done - when people do this, they should get the death penalty".

17:40

Trump stands by gun control stance

Donald Trump has briefly spoken to reporters following the shooting - and said the incident had nothing to do with gun laws in the US.

"If they had protection inside, the results would've been far better," he said.

"This is a dispute that will always exist, I suspect. But if they had defences inside the temple, things could've been different."

On whether churches and synagogues could have armed guards, he said it was "certainly an option".

He praised the response of the police as "outstanding" and said those responsible for such attacks should face the death penalty.

He said: "Some people disagree with me, I can't imagine why. This has to stop."

17:35

Shooting 'more devastating than originally thought'

Donald Trump has tweeted for the second time since the shooting took place at around 10am local time.

"Events in Pittsburgh are far more devastating than originally thought," he said.

"Spoke with Mayor and Governor to inform them that the Federal Government has been, and will be, with them all the way. I will speak to the media shortly and make further statement at Future Farmers of America."

17:27

Key points:

At least eight dead in synagogue attack in Pittsburgh, Pennsylvania - US media

Three police officers injured in incident at Tree of Life Synagogue

Shooter is in custody but locals warned to stay indoors

Donald Trump says he is "watching the events unfolding in Pittsburgh"

Police deployed to other synagogues as precaution

17:25

'At least eight dead' - US media

NBC News and CBS News are reporting that at least eight people are dead as a result of the shooting.

At least 12 have been injured, three of whom are police officers, they say.

NBV is also reporting that the suspect was armed with an AR-15-style rifle and multiple handguns.

17:21

Police deployed to other synagogues

The New York Police Department says it has deployed officers to synagogues throughout the city as a precaution.

The synagogue that was attacked was holding a shabbat religious service at the time, according to its website.

17:14

WATCH: 'Stay inside, it's not safe'

17:12

'This is a highly-charged situation'

Sky's US correspondent Amanda Walker reports: "This is still a very raw and chaotic situation as police try to deal with what has happened here.

"There is no word (on motive) from police yet, but people will be looking at the location. This is a very highly-charged situation in the US at the moment, if you look at the mail bomb campaign over the past week.

"We know the suspect in that case held some pretty right-wing views and there are certainly some highly-charged views in this country at the moment."

17:03

'The violence needs to stop'

First Lady Melania Trump has followed her husband by tweeting a response to the shooting.

My heart breaks over the news out of Pittsburgh," she said.

"The violence needs to stop. May God bless, guide & unite the United States of America."

17:00

WATCH: Armed officers at scene of shooting

16:57

'At least four dead' - US media

According to Reuters, local TV station KDKA and CNN are both reporting that at least four people have been killed in the shooting.